Abstract. The inaccuracy of anthropogenic emission inventories on a
high-resolution scale due to insufficient basic data is one of the major
reasons for the deviation between air quality model and observation results.
A bottom-up approach, which is a typical emission inventory estimation method,
requires a lot of human labor and material resources, whereas a top-down
approach focuses on individual pollutants that can be measured directly as well as
relying heavily on traditional numerical modeling. Lately, the deep neural
network approach has achieved rapid development due to its high efficiency and
nonlinear expression ability. In this study, we proposed a novel method to
model the dual relationship between an emission inventory and pollution
concentrations for emission inventory estimation. Specifically, we utilized a
neural-network-based comprehensive chemical transport model (NN-CTM) to
explore the complex correlation between emission and air pollution. We further
updated the emission inventory based on back-propagating the gradient of the
loss function measuring the deviation between NN-CTM and observations from
surface monitors. We first mimicked the CTM model with neural networks (NNs)
and achieved a relatively good representation of the CTM, with similarity
reaching 95ā%. To reduce the gap between the CTM and observations, the NN
model suggests updated emissions of NOx, NH3, SO2, volatile organic compounds (VOCs)
and primary PM2.5 changing, on average, by ā1.34ā%, ā2.65ā%, ā11.66ā%,
ā19.19ā% and 3.51ā%, respectively, in China for 2015. Such
ratios of NOx and PM2.5 are even higher (ā¼ā10ā%) in regions that suffer from large uncertainties in
original emissions, such as Northwest China. The updated emission inventory can improve model
performance and make it closer to observations. The mean absolute error for
NO2, SO2, O3 and PM2.5 concentrations are reduced
significantly (by about 10ā%ā20ā%), indicating the high
feasibility of NN-CTM in terms of significantly improving both the accuracy
of the emission inventory and the performance of the air quality model.